Present invention relates to a heat-resisting alloy for rolls, and particularly to glass forming roll, continuous casting roll or such rolls to which severe heating and cooling are repeated.
Plate-like glasses are manufactured by means of a glass forming rolling machine by having molten glass pass the roll continuously. However, the surface of roll is heated to approximately 700.degree. C. by contacting with molten glass of high temperature and is subject to oxidation. The surface of roll is cooled by passing water in the hollow portion of the roll inside to prevent it from high temperature oxidation, however, the portion where molten glass does not contact is cooled with air. Since the roll of a glass forming machine is thus subject to heat impact by heating and cooling, heat cracks are apt to be generated on the roll surface in short time of operation, which obliges replacement of the roll.
In the roll for continuous casting, the roll surface contacts with slab of high temperature and is subject to high temperature oxidation. Heat cracks are also found on the surface of the roll in short period of operation due to repetitions of heating and cooling.
Rolls working in the high temperature have basically same problems, therefore, glass forming roll will be described in detail.
In view of resistance to oxidation and to heat cracks, Cr-Mo steel containing 0.10 to 0.15% (by weight, the same as hereinafter) of C, 1.0 to 2.0% of Cr, 0.10 to 1.5% of Mo, or Ni-Cr steel containing 0.10 to 1.15% of C, 1.0 to 2.0% of Ni, 0.10 to 1.0% of Cr, or ductile cast iron or the like have been used as roll materials for glass forming. Those materials are not sufficient to prevent generation of rough surface and heat cracks on the circumferential face of rolls. Such rough surface or heat cracks generated on the roll surface are transferred to the glass surface in the course of glass forming process, and thus glass of fine surface is not produced with such forming rolls.